From Harry Potter and The Half Blood Prince we can know that Voldemort wished to make 7 Horcruxes. But we know that Voldemort's 7 Horcruxes included Harry. But as this was unintentional, Voldemort didn't know about this.

Didn't Voldemort (his original body) perish while attempting to kill Harry? So even if he did want to create another Horcrux (answers notwithstanding), he was kind of out of the picture at that point, yes?
– Jesse C. SlicerApr 9 '18 at 16:36

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@WillemVanOnsem this question already has an answer there, so it would be a duplicate. Also note that just because it might be a better fit on another site, that doesn't make it off-topic for this one.
– JADApr 10 '18 at 8:27

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@WillemVanOnsem yep, happens a lot, especially with Harry Potter and Game of Thrones
– JADApr 10 '18 at 8:29

3 Answers
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You made the same mistake as Harry in Harry Potter and The Half Blood Prince. As JAD said, Voldemort wanted to split his soul in seven, not create seven Horcruxes (emphasis mine):

“[...] You heard him, Harry: ‘Wouldn’t it be better, make you stronger, to have your soul in more pieces... isn’t seven the most powerfully magical number...’ Isn’t seven the most powerfully magical number. Yes, I think the idea of a seven-part soul would greatly appeal to Lord Voldemort.”

“He made seven Horcruxes?” said Harry, horror-struck, while several of
the portraits on the walls made similar noises of shock mid outrage. “But they could be anywhere in the world — hidden — buried or invisible —”

“I am glad to see you appreciate the magnitude of the problem,” said Dumbledore calmly. “But firstly, no, Harry, not seven Horcruxes: six. The seventh part of his soul, however maimed, resides inside his regenerated body. [...]”